Nature of yrast excitations near N=40: Level structure of Ni-67

Excited states in Ni-67 were populated in deep-inelastic reactions of a Ni-64 beam at 430 MeV on a thick U-238 target. A level scheme built on the previously known 13 micro-s isomer has been delineated up to an excitation energy of ~5.3 MeV and a tentative spin and parity of (21/2-). Shell model calculations have been carried out using two effective interactions in the f5/2pg9/2 model space with a Ni-56 core. Satisfactory agreement between experiment and theory is achieved for the measured transition energies and branching ratios. The calculations indicate that the yrast states are associated with rather complex configurations, herewith demonstrating the relative weakness of the N=40 subshell gap and the importance of multi particle-hole excitations involving the g9/2 neutron orbital.Comment: Accepted by Physical Review

Experimental study of neutron-rich nuclei 89Rb and 91Rb

Neutron-rich 89,91Rb nuclei populated as fission products in heavy-ion reactions have been studied with the Gammasphere array. The previously known level schemes have been extended to higher excitation energies and spins. Spin and parity assignments were based on angular correlation analyses. A value of T1/2 = 8(2) ns was extracted for the isomeric g9/2 state in 89Rb

Low-energy structure of 61Mn populated following β\beta decay of 61Cr

$\beta$ decay of the $^{61}$Cr$_{37}$ ground state has been studied. A new half-life of 233 +/- 11 ms has been deduced, and seven delayed $\gamma$ rays have been assigned to the daughter, $^{61}$Mn$_{36}$. The low-energy level structure of $^{61}$Mn$_{36}$ is similar to that of the less neutron-rich $^{57,59}$Mn nuclei. The odd-A $_{25}$Mn isotopes follow the systematic trend in the yrast states of the even-even, Z + 1 $_{26}$Fe isotopes, and not that of the Z - 1 $_{24}$Cr isotopes, where a possible onset of collectivity has been suggested to occur already at N = 36.Comment: 19 pages, 7 figures, accepted to Physical Review

β Decay and isomeric properties of neutron-rich Ca and Sc isotopes

The isomeric and β-decay properties of neutron-rich Sc53-57 and Ca53,54 nuclei near neutron number N=32 are reported, and the low-energy level schemes of Sc53,54,56 and Ti53-57 are presented. The low-energy level structures of the 21Sc isotopes are discussed in terms of the coupling of the valence 1f7/2 proton to states in the corresponding 20Ca cores. Implications with respect to the robustness of the N=32 subshell closure are discussed, as well as the repercussions for a possible N=34 subshell closure

Low-energy structure of Mn61 populated following β decay of Cr61

β decay of the Cr6137 ground state has been studied. A new half-life of 233±11 ms has been deduced, and seven delayed γ rays have been assigned to the daughter Mn6136. The low-energy level structure of Mn6136 is similar to that of the less neutron-rich Mn57,59 nuclei. The odd-A25Mn isotopes follow the systematic trend in the yrast states of the even-even, Z+1 26Fe isotopes, and not that of the Z-1 24Cr isotopes, where a possible onset of collectivity has been suggested to occur already at N=36

Single-neutron states in Sn101

The first data on the relative single-particle energies outside the doubly magic Sn100 nucleus were obtained. A prompt 171.7(6)keV γ-ray transition was correlated with protons emitted following the β decay of Sn101 and is interpreted as the transition between the single-neutron g7/2 and d5/2 orbitals in Sn101. This observation provides a stringent test of current nuclear structure models. The measured νg7/2-νd5/2 energy splitting is compared with values calculated using mean-field nuclear potentials and is used to calculate low-energy excited states in light Sn isotopes in the framework of the shell model. The correlation technique used in this work offers possibilities for future, more extensive spectroscopy near Sn100